Inhibitory effect of mutastein on the synthesis of artificial, dental plaque by Streptococcus mutans.

Fig. 1. Effect of mutastein on the formation of artificial plaque on Nichrome-steel wires by Streptococcus mutans 671 5. Experimental conditions were described in the text. 1; Control, 2; 15 ^g/ml mutastein, 3; 50 ^g/ml mutastein. It is believed to be a significant step for the induction of dental caries that cariogenic Streptococcus mutans synthesizes adhesive, insoluble glucan from sucrose and adheres to tooth surfaces to form dental plaque in the oral cavity0. This is supported by the fact that mutant strains of $. mutans defective in adhesive glucan synthesis lack cariogenicity0. Thus, inhibition of the synthesis of the adhesive, insoluble glucan is expected to be an effective means for preventing plaque formation and caries development. Mutastein, a heat-stable glycoprotein isolated from the culture filtrate of Aspergillus terreus, was identified as a specific inhibitor of glucan synthesis2). This substance suppresses significantly plaque formation and caries development in rats3), and is nowused commercially as a protective agent against caries development in humans. Two glucosyltransferases (GTase) are known to be involved in the glucan synthesis by S. mutans, one (GTase-S) that catalyzes soluble glucan synthesis and one (GTase-I) that converts soluble glucan to the adhesive, insoluble glucan4). Mutastein was reported to inhibit the latter enzyme of several strains of S. mutans2>5\ In the present experiments, the inhibitory effect of mutastein on glucan synthesis in the cell-free enzyme system of S. mutans 6715 and the formation of artificial, dental plaque by growing cells of this strain were studied. Mutastein was isolated from the culture filtrate of A. terreus as described previously2). Briefly, the culture filtrate was adjusted to pH 3.5 with HC1 and the resultant precipitate was collected by centrifugation. The precipitate was * Present address: Central Research Laboratory, Godo Shusei Co. Ltd., Matsudo-shi, Chiba-ken 271, Japan. submitted to ammoniumsulfate precipitation and chromatography of hydroxyapatite and Toyopearl HW-65. Cell-free extracts of S. mutans 6715, containing both GTase-S and GTase-F\ synthesized adhesive, insoluble glucan along with small amounts of nonadhesive, insoluble glucan and soluble glucan (Table 1). Mutastein inhibited adhesive, insoluble glucan synthesis by 45%at a concentration of 0.1 pgjm\ and almost completely at 0.4 ^g/ml. On the other hand, synthesis of both nonadhesive, insoluble glucan and soluble glucan was markedly stimulated by mutastein; the activation was 3-fold for the former and 10-fold for the latter at a mutastein concentration of 0.4 ^g/rnl (Table 1). The data suggest that mutastein inhibited specifically the conversion of soluble glucan to adhesive, in-